An action for a grand piano, including a repetition lever, is generally configured as follows: The action of a grand piano is provided in a manner pivotally movable about a rear end thereof, and includes a wippen disposed on a rear part of a key, and a repetition lever and a jack which are pivotally mounted to the wippen. The repetition lever is mounted to the wippen in a state engaged with a bifurcated lever-mounting part of the wippen. The repetition lever extends in the front-rear direction, and a hammer is disposed on an upper surface of the repetition lever via a shank roller. The upper end of the jack is engaged in a jack guide hole formed in the repetition lever, and is opposed to the shank roller from below with a slight space therebetween in a key-released state. Further, the repetition lever and the jack are urged in a returning direction by a repetition spring, and in the key-released state, the jack is opposed to a regulating button from below with a slight space therebetween.
With the arrangement described above, when the key is depressed, the wippen is pushed up, whereby the repetition lever and the jack are pivotally moved upward along with the wippen. With this pivotal motion, the jack pushes up the hammer via the shank roller. Thereafter, when the hammer pivotally moves immediately close to a position for striking a string stretched above, the jack comes into engagement with the regulating button to be released from the shank roller. This disconnects the hammer from the action and the key and causes the hammer to strike the string in a free rotation state. After having struck the string, the hammer pivotally moves in the opposite direction.
Then, when the key is released, the repetition lever is pivotally returned by the resilient force of the repetition spring to thereby push up the hammer via the shank roller in timing in which the key is returned to a predetermined height. As a consequence, the jack is pivotally returned by the resilient force of the repetition spring to be positioned under the shank roller, whereby a following string-striking operation can be reliably performed even when the key is not completely returned. This ensure the capability of repeated key striking.
As is apparent from the above, the repetition lever is a component part for pushing up the hammer via the shank roller after the hammer has struck the string, so as to attain repeated key striking, such as a trill in which the same key is repeatedly struck. Conventionally, in general, the repetition lever is made of wood, similarly to many other action component parts. This is because wood is advantageous in that it is easily available and excellent in machinability as well as highly rigid in spite of its light weight. In particular, the repetition lever is required to be not only light in weight for making pivotal motion lightly with quick response to key release so as to push up the hammer in predetermined timing responsive to the key release, but also highly rigid so as to prevent the repetition lever from being largely warped during the operation of pushing up the hammer.
Further, a conventional repetition lever made of a synthetic resin has been disclosed e.g. in Patent Literature 1. This repetition lever is made of an ABS resin etc., and has a conductive coating or metal layer formed at least on a surface thereof so as to prevent the repetition lever from being electrostatically charged.
As described above, wood is generally used as a material for the conventional repetition lever because wood is not only light but also high in rigidity. However, since wood, which is a natural material, lacks homogeneity, it suffers from variations in rigidity and weight, and is prone to deformation, such as warpage or distortion, due to residual stress. Further, wood undergoes large dimensional change due to dryness and wetness, and hence relatively large transverse expansion or contraction of the repetition lever occurs depending on humidity. As a result, the clearance between the lever-mounting part of the wippen and the repetition lever changes, which loosens or tightens engagement between the repetition lever and the wippen. The deformation of the repetition lever and the change in clearance between the lever-mounting part of the wippen and the repetition lever can make the operation of the repetition lever unstable.
On the other hand, in the case where the repetition lever is made of the ABS resin as disclosed in Patent Literature 1, since the ABS resin is excellent in shape retainability and dimensional stability, the above described problems with the wooden repetition lever cannot occur. Further, the repetition lever made of the ABS resin is advantageous in that it can be machined with high accuracy and material costs can be reduced. However, since the ABS resin has a larger specific gravity than wood, the lightness of the repetition lever is impaired, which makes its motion slow. Further, since the ABS resin has a lower rigidity than wood, the repetition lever made of the ABS resin is largely warped in pushing up the hammer, which causes a lag in timing in which the hammer is pushed up. Thus, the advantages of the wooden repetition lever are lost, and hence the capability of repeated key striking is degraded.
The present invention has been made in order to solve the above problems, and an object thereof is to provide a repetition lever for a grand piano, which is excellent in shape retainability and dimensional stability and is light in weight and high in rigidity, thereby enabling required operations to be stably performed and improving the capability of repeated key striking.
[Patent Literature 1] Japanese Laid-Open Patent Publication (Kokai) No. 2003-5740